The present invention is directed to an apparatus for controlling fluid flow rate. More particularly, the invention relates to a variable infusion device for administering liquids parenterally to a patient.
The administration of liquids parenterally to a patient is a treatment that has been employed for many years. It typically involves the use of a container of liquid to be infused, an elongated flexible tube for conveying the liquid from the container to a patient and a cannula or catheter for insertion into the cardiovascular system of the patient to introduce the liquid for infusion into the patient's system. A variety of liquids may be infused in this manner, including dextrose, saline, Ringers solution, and water or any combinations of these solutions. Others include whole blood and plasma. More recently, drugs such as antibiotics, heparin, etc. are administered in this manner.
In past, the most common manner of controlling the flow of the liquid being administered to the patient has been to selectively collapse a portion of the flexible delivery tube using a roller clamp, for example. The rate of flow in such cases is determined by the rate at which drops of liquid are observed falling through a conventional drip chamber. While this arrangement for administering liquids parenterally has been satisfactory where the desired flow rates are comparatively fast and the accuracy of the flow rate is not crucial, it is not suitable where very accurate or very low flow rates are necessary as, for example, where a drug must be administered to a patient at a very low constant flow rate over an extended period of time or where a very low flow rate is desired merely to keep intravenous cannulas and catheters from becoming clogged with clotting blood until further administration of liquid medications is desired.
An object of the present invention is to provide a variable infusion device for administering liquid parenterally to a patient which avoids the aforementioned drawbacks of this known arrangement for controlling the flow of parenteral fluids to a patient. More particularly, an object of the invention is to provide a variable infusion device for administering liquids parenterally which may be placed at any point in a supply line between a container of liquid to be administered to a patient and the patient for accurately controlling the liquid flow rates over extended periods of time at a desired flow rate which may include very low flow rates.
A further object of the invention is to provide a variable infusion device for administering liquid parenterally to a patient which regulates the flow of liquid by selectively varying the effective length of the flow passage through the device.
An additional object of the invention is to provide a variable infusion device for administering liquid parenterally to a patient which can be manufactured at relatively low cost with a minimum number of parts for economical use in a wide variety of applications.
These and other objects of the invention are attained by the variable infusion device of the present invention which comprises means defining an elongated passage through which a liquid can be flowed, and means for changing the flow rate of a liquid flowing through the elongated passage. The means for changing the flow rate includes means for changing the length of the elongated passage through which the liquid is flowed thereby changing the flow rate of the liquid. The means defining an elongated passage includes a first member having an elongated groove with a small cross-sectional area formed in a surface thereof and a second member having a surface overlying the groove. The means for changing the length of the elongated passage through which the liquid is flowed comprises a third member having means for selectively bypassing the liquid about at least a portion of the elongated passage defined between the first and second members through a bypass passage. The first and second members are secured against movement relative to one another in the device. As a result, an effective liquid seal about the elongated passage between the first and second members can be maintained even in the case both members are formed of a plastic material, for example. According to the preferred embodiment, the first and second members are bonded to one another. The third member is formed of an elastomeric material which is pressed against a surface of one of the first and second members to form a liquid seal therewith, while permitting relative movement between the third member and the assembly of the first and second members for selectively bypassing the liquid about at least a portion of the elongated passage defined between the first and second members.
At least one of the first and second members has a plurality of spaced openings communicating with respective portions of the elongated passage defined between the first and second members. The third member is movable relative to the spaced openings to selectively communicate a bypass passage with respective ones of the openings to thereby change the length of the elongated passage through which liquid is flowed. The third member closes the other openings while communicating a selected one of the openings with the bypass passage. In the disclosed embodiment, the first, second and third members are retained within a dial cover of the device.
The disclosed variable infusion device also includes a fourth member having an additional elongated groove formed in a surface thereof. An additional surface of the second member overlies the additional groove. The second member is secured against movement relative to both the first and fourth members. In the preferred form of the invention, the second member is bonded to both the first and fourth members to form an assembly. The assembly is mounted upon a connector housing of the device via the fourth member. The connector housing is provided with an inlet and an outlet at the respective ends of the means defining an elongated passage for communicating liquid to for from the device. The second member of the device is preferably formed of a plastic material which is chemically bonded to the first and fourth